250SX still running badly at WOT....

[Big Sal]

Hey guys, still can't get the SX to go wide open without bogging and backfireing....when I push the throttle all the way it boggs, backfires a couple times, revs up then boggs and backfires a few times then revs...well, you get the picture...lol. It actually gets a little worse with the choke on....I put in a new plug, cut the very end off the coil wire (on the boot side) to make sure it was good, cleaned the carb out for the umpteenth time, tank is clean (I creamed it) fresh gas, made sure everything was tight and still the same thing...looking for suggestions where to go next....on a different note.....what do you guys think a 83 Big Red 200 with possible stator problems is worth? It's in fairly good condition and looks complete...said it ran great when parked a year ago...I'm thinking gummed carb and tank along with bad gas...I can get it for $350....

[atc007]

CDI box. Assuming you DO have the carb right. I'd be looking at the CDI. Let us know.

[Big Sal]

I was thinking the same thing....just wanted to see if anyone else thought so....i'll check all my connections and grounds....

[Big Sal]

Well I got a CDI on the way....let's see if this corrects the problem...

[Big Sal]

Got the replacement CDI and it's still running the same....bogging, backfiring the whole 9 yards at full throttle...what else could possibly cause this? I've cleaned the carb, rebuilt it, set it to factory, increased the needle setting one notch richer (thinking it was a lean condition) new plug (now it's black like it's running rich)...it starts fine, and runs ok (it will bog if you stab the throttle to hard)...but won't wind up. Do the factory CDI's have a rev limiter??? It also has the thumb throttle and cable from a big red the same year, would that make a difference? The diff is also from the big red donor, would the different gear ratio affect it? I'm really banging my head against the wall on this one....

[atc007]

None of the BR stuff would do this.. Loose,bare , or bad ,ground wire at the Coil itself? That will do exactly this,,but VERY rare! Any bad ground. I would then check the ohm readings on your stator. I still suspect carb,,but taking your word for it the carbs right.. This goes with the carb,,but I can assume Nothing!! you DID clean your tank out? Your petcock can be plugged ,,letting enough fuel thru to run and idle all day,,But when the need increases ,the fuel flow can't . IF you have not,,clean your petcock out! That's what it is isn't it !

[Big Sal]

The fuel system has been cleaned out (I had to cream the tank due to rust and pinholes) so the tank is spotless inside, but I'll definitly check the petcock again. The battery stays charged and the lights are nice and bright, so I never gave the stator a thought. I changed the coil to another used one (again off my donor BR) with no change...I suspected the carb too, but I've cleaned, soaked, blown out and all that good stuff so many times it's just gotta be clean...I did rebuild it with a Moose rebuild kit, I've heard good and bad things about them...it does good as long as I don't get to throttle happy (stabbing the throttle to hard or pushing it to the limit) it's ridable the way it is, but I hate when things aren't right...lol

[murfman]

Sounds like a carb/fuel issue for sure, are you absolutely sure every passage and jet is clean and clear in the carb? I soaked the parts of my carb overnight in a parts dip can I bought at autozone and then sprayed out every passage with carb cleaner followed by compressed air. I'd double check the main jet and the passages associated with it. As stated above are you sure the petcock is clear? I run transparent fuel line so I can see the fuel going to the carb and an inline filter just to be sure as well. Stupid question, but you do have the vent open on the cap, don't you?

[tri again]

The only other oddity sx specific mentioned is....
some wire near the battery box that flexes with the suspension
and has intermittent or commitment issues for current or continuity.

I have NO idea what the symptoms are but always heard to look at that
part of the wire harness.

I feel for you man.

The thing I missed 2X was an emulsion tube that hides under one of the screw out jets.
It's about an inch long, full of holes and packed with rust muck.
I tried to pick it out with a dental tool but wound up getting it out with a round toothpick.

Worst case isn't too bad..... my 2nd to last sx has an aftermkt Keihin with a regular flapper choke and accel pump.
and is really quite refreshing.
I posted the Keihin numbers a couple weeks ago but can do it again if you can't find them.

Valve lash throwing valve timing off?
Where do these get their spark advance from?
Is there a plate that rotates could be stuck?

Puh Lease let us know what you find.

Oh PS
I had a carb kit or 2 that the float needles were DIFFERENT lengths and said
250sx on them.
Float level? I run mine with the gas off all the time and it runs GREAT until it dies so IDK
but I feel your pain.

[Big Sal]

I found that tube...lol...cleaned it real good...soaked the carb and blew it out. I assumed with a CDI it didn't have a mechanical advance..I'm gonna go thru the harness and check everything AGAIN...lol. The thing was under a tarp, out in the weather for 5 years, so I guess I'm lucky it runs at all, I'm driving myself nuts because I like things to run perfect or as close to perfect as possible...the stumble from stabbing the throttle I could live with.....the bogging at WOT bothers me....quick note...if I back out of the throttle it does clear up, but getting back into it and putting it under a load produces the same effect no matter what gear I'm in, including neutral.... I hate to invest in a replacement carb, only to find out the problem is still there. I was hoping it was something stupid that I overlooked, or didn't think would cause it. The gas cap vent is open and clear....the previous owner did something at one point and melted the black mud flap on the front fender...which means to me that exhaust got really, really hot...I hope that's not part of the problem.

[tri again]

MICE??
Ol' critter nest in the exhaust or collapsed
baffel rust bucket muffler?

Half of my flaps are melted too but almost asked why one time.
They say lean condition causes excessive heat, among other things.

Have you tried the search key?

[tri again]

The cdi has the advance Curve but not sure where the actual spark advance comes from.
Of the 8 or 10 250 's I have, never had to even think about it.

Also know what you mean.
1/2 kick to start.
Idle like a dream
and runs PURfectly over all throttle ranges and actually scary fast when asked to be.

That stuff drives me absolutely nutts too.
Mouse nest in airbox?
" "" muffler?
valves adjusted ok?
Compression good?

Ya gotta find out what's wrong and tell us.

[Big Sal]

Nope, the exhaust seems to be clear....there is plenty of it coming out of the muffler...it did it with the rusted out muffler too...I thought it wasn't getting enough back pressure. I bought one off a running unit that was parted out. It really ran bad before I put the airbox to frame rubber air intake tube back on....that made it run better.

[SYRacing]

sounds dumb, but check the spark plug gap. If it's too wide (as the plugs often come when new) the coil doesn't have enough power to jump the wider gap at higher RPM's.

[Big Sal]

Maybe I have to bite the bullet and buy a carb....

[Big Sal]

plug gap set to factory spec...I never trust the gap on new plugs...lol

[tri again]

Maybe I have to bite the bullet and buy a carb....

Not easy to find, especially with the choke piston intact.
The QA01 was the first gen carb and had cold start issues so a later one QA02 or way later up to 1987 is good
or that aftermarket one I got with my second to last sx with the accelerator pump is a freakin' rocketship dream.
Old stye flip flapper choke too.

Are we sure it's not electrical breakdown?
bad frame grounds? They are Everywhere on the diagram but not real sure
where they are on the machine.
The kill switch has a ground TO kill it and also the cdi gets it's ground from that same circuit for it TO run...
as I recall...unless I'm mixing up my trike models.

The only thing I remember is going blind tracing that sucker down.

Should I look for the stock jets sizes I wrote down the last time I went thru my carb?

[tri again]

Maybe I have to bite the bullet and buy a carb....

Not easy to find with intact choke plunger.
Sorry if this is a duplicate. system crashed.
Sure it isn't electrical breakdown?
The cdi gets it's ground to KILL it and also gets the ground for it TO run from the same circuit,
unless I've got my trike models mixed up.

Grounds are everywhere on the diagram but not sure where on the machine itself.

Carbs QA01 is the first gen with a cold start issue so QA02 and later is better up to 1987.
Do you want me to check my stock jet sizes I wrote down my last trip thru?

Also my aftermarket sx carb is a dream. Flapper choke and accel pump.
I can get you those numbers too.

[atc007]

I tried to get to page 2,,but I'm getting the forbidden page ? Anyhow,,,put your stock 3 jets back in the carb. MAking sure they are blown out clean.. I wouldn't trust that carb kit,,,some work ok,,some don't at all. I would clean and check that petcock,,make SURE there is a solid steady,long flow of fuel. Then the Honda jets back in the carb. You'll get it ,don't get discouraged! And when you're done,,,everything will just purr. !

[Big Sal]

Well I found out something....if I take my hand and squeeze off the intake tube from the frame to the airbox the darn thing takes off like a raped ape....so is this a main needle adjustment or do i have to install bigger jets??

[350xx]

Buy a new carb from WINCYCLES, their store is also on ebay.
Just a suggestion. bcause theyre cheap

[Big Sal]

only way to see page 2....lol

[dreux13]

Hey Big Sal, What was the ultimate fix for this? I'm in the exact same boat as you were on this and I'd kill to know what the fix was. Was it ground or new carb? No one ever posts what the fix was on the forums!

Thanks and hope this finds you well 3 years later!